1. Field of the Invention
This invention is broadly concerned with a measuring tool for collecting down hole information and a metering valve for producing a so-called mud-pulse used in the measuring tool and intended particularly to be used in a technology to collect data at a down hole of a vertical/inclined shaft which is dug to construct petroleum wells, geothermal wells or natural gas wells, or for seismic observation or geological survey.
2. Description of the Related Art
Several types of vertical shaft have previously been dug underground to construct petroleum wells, geothermal wells or natural gas wells, or for seismic observation or geological survey.
These shafts are generally made by rotation of a long and narrow drilling pipe having a drilling bit at its forward end. The drilling pipe is adapted to flow a mud-flow thereinside.
The mud-flow is transferred through the interior of the drilling pipe from ground level and then fed out at the lower most portion of the drilling pipe (i.e., the drilling bit), prior to returning to the earth's surface through a space between the drilling pipe and the vertical shaft. Such circulation of the mudflow can move and discharge to the ground level unnecessary articles from down hole, such as stones, rocks and sediment by means of water flow. When the shaft depth is in the range of 5,000 meters, the mud-flow carried from the down hole is generally high in temperature due to geothermal heat and water pressure.
It is noted that information, about load to the bit and conditions such as pressure, temperature, bit road and bit torque and temperature at the down hole, should be continuously and closely observed throughout the drilling operation. Accordingly, a measuring tool which can collect various information at the down hole and transmit same to ground level is known.
There are two known types of conventional down hole information collecting devices, one being a permanent-type which can be fixed relatively near the drilling bit until the drilling operation is completed, the other being of a retrievable-type which can be retrieved to ground level from the down hole when necessary, but only a main part of the other down hole information collecting device can be retrieved.
The permanent-type down hole information collecting device is so arranged that plural sensors and a main part thereof are associated into a bitsub as an auxiliary pipe to connect the drilling bit with the long drilling pipe.
The retrievable-type down hole information collecting device comprises a sonde containing therein the plural sensors and the main part all together. This sonde is provided with the bitsub separately so that it can be withdrawn to ground level by using wire rope.
As each sensor is electrically and directly related with the drilling bit in the permanent-type down hole information collecting device, it will be observed that such useful data for the drilling bit as torque and load can be measured comfortably, but the device can not be withdrawn to the ground even when a temperature at the down hole will become extremely high, so that the device will be badly influenced and broken down sometimes.
While the retrievable-type down hole information collecting device will not be damaged by unforeseen heat, pressure and the like, since the sonde can be withdrawn from the down hole to the ground level, but a preferable electrical connection between the sonde and the sensors installed in the drilling bit may not be ensured whereat information around the drilling bit can not be collected reliably.
The such down hole information collecting device is generally provided with a mud-pulse generating device to transmit down hole information to the ground level. The mud-pulse generating device has a function to send information to the ground by means of pressurized pulse which propagates the information through the mud-flow fed into the drilling pipe.
The above-mentioned device employs a metering valve which can quickly wring a flow rate of the mud-flow so as to generate the pressurized pulse. One of known typical metering valve employs a mechanical type switching valve where a port passing therethrough the mud-flow is opened and shut repeatedly by using a plug.
However, it has been noted among persons in the art using the mentioned conventional mechanical type metering valve that relatively large port and corresponding plug were necessary to keep enough flow rate of the mud-flow, which naturally caused uncomfortable transmitting of the pressurized pulse and waste of electrical power when operating the metering valve, because of a heavy weight of the plug and a resistance raised by the mud-flow.
A slight opening immediately before and after a complete closing of the associated port and plug may cause a high speed flow of the mud-flow to thereby wear respective surfaces of the associated members. Furthermore, the presence of some articles containing the mud-flow between the port and the plug may cause severe problems by unforeseen shock and vibration of the drilling bit.
The present invention aims to provide a measuring tool which can collect information near the drilling bit in a vertical/inclined shaft and which is so arranged that a main part thereof can be retrieved to the ground if necessary.
Another object of the present invention is to provide a metering valve which can generate pressurized pulse securing a high transmitting rate with a little electrical power and which can produce mud-pulse in the tool with no troubles.